A turbine can provide a highly efficient means for converting energy within a moving fluid into torque. The fluid is typically directed against blades that absorb energy from the fluid by deflecting the flow. Blades are mounted radially on a central rotor that rotates in response to energy imparted to each blade by the fluid. Blades may be grouped in stages along the length of a rotor, with the shape of the blades in each stage selected to optimize energy transfer under expected fluid conditions.
Since a turbine usually obtains highest efficiency at high rotational speed, the blades and rotor require precision machining and must be carefully balanced. Blades may expand and warp when heated and are subject to chemical and mechanical damage. Resulting imbalances may destroy a turbine. The rotor in a reaction turbine is often supported by bearings that are subject to extreme temperatures and corrosive agents, also causing turbine failure. The exotic materials and precision manufacturing needed to ensure both maximum efficiency and reliability result in high manufacturing and maintenance costs.
The Tesla turbine was an early attempt to avoid design problems inherent in a turbine utilizing blades. The Tesla turbine instead utilizes of a set of parallel disks mounted radially on a shaft. One or more nozzles direct a moving fluid toward the outer edges of the disks. As the fluid passes between disks, adhesion between the fluid and each disk transfers energy from the fluid to the disks, which in turn apply torque to the shaft. Since the fluid is exhausted from the turbine through ports near the shaft, fluid flowing between disks spirals inward, maximizing contact time and energy transfer.
Although the Tesla turbine is in theory highly efficient, maximum efficiency is achieved when the spacing between disks approximates the thickness of a particular fluid's boundary layer. Since boundary layer thickness varies with fluid pressure and viscosity, each Tesla turbine design must be optimized for a specific range of fluid conditions. Disks must be thin to maximize available surface area and minimize edge turbulence. Disks must be closely spaced to maximize energy absorption from low viscosity fluids. Thin, closely-spaced disks may be subject to warping and damage.
What is needed is a turbine that avoids these shortcomings, is inexpensive to manufacture and maintain, and is able to extract energy from a variety of moving fluids over a wide range of temperature, pressure, viscosity, and chemical conditions without suffering significant damage.